The UN refugee chief said today he has never seen "such toxicity, such poison" in politics, the media, social media and every day conversation focused on refugees, migrants and foreigners.

UN High Commissioner for Refugees Filippo Grandi said the March 15 attack on a mosque in Christchurch that killed 50 Muslim worshippers was the result "of that toxic language of politics".

Grandi urged countries everywhere to take "a leaf from the exemplary response of the people and the leadership of New Zealand" in responding to the "toxic trends" by restating the values that underpin global solidarity and "reaffirm that our societies will not be really prosperous, stable and peaceful if they do not include all".

An Australian white supremacist who has been charged with the mosque killings which included many immigrants, livestreamed the shootings and sent out a lengthy manifesto.

Prime Minister Jacinda Ardern has said the world has been stuck in a vicious cycle of extremism which must end, and she will never utter his name and give his views the oxygen he wanted.

Grandi told the Security Council "there is unprecedented stigmatisation of refugees and migrants," and responses are increasingly inadequate.

He said he has worked with refugees for over three decades and has seen "much solidarity, even heroism in some of the responses that are provided on the ground" to help them.

And "that solidarity is still very strong" in many parts of the world, from African villages to the border between Bangladesh and Burma, to communities in Latin American helping Venezuelans, Grandi said.

"But also in these 3 1/2 decades I have never seen such toxicity, such poison in the language of politics, in media, in social media, even in everyday discussions and conversations around this issue — toxicity that focuses sadly, tragically, often, on refugees, on migrants, on foreigners," he said.

"That should be of concern to us all."

Grandi added that "many politicians believe that — and I think they are proven right — that doing this expands their consensus."

But he said this is wrong and unfair to people "that are fleeing because they seek safety from war, from persecution."

He said the mosque attacks showed this has become an issue of security and stability for all countries — and governments need to address the issue of language on social media and in politics.

"It is an issue if left unchecked may have very grave consequences, not only for our work but for the world in general," Grandi warned.